Summary:
TransactionReplicator replicates transactions on follower machines in
HA memgraph. Our DB accessor API doesn't provide us with the functionality to
begin transactions with non-increasing ids. This is why the
`TransactionReplicator` uses a internal map that maps tx ids from the leader
node to transactions on the follower node (whose id doesn't have to match the
leaders tx id).
If the leader has the following transaction timeline:
```
L
tx1
|
| tx2
| |
| |
| |
| |
| |
| tx2
|
|
|
|
tx1
```
`tx2` will commit first and will be replicated. When applying `tx2` on follower
nodes, they will start a new transaction with tx id `1`. When `tx1` starts
replicating, followers will start a new transaction with tx id `2`. And this is
wehre `TransactionReplicator` kicks in.
Reviewers: ipaljak
Reviewed By: ipaljak
Subscribers: pullbot
Differential Revision: https://phabricator.memgraph.io/D1775
5e6cf0724a